The present invention relates to interconnect assemblies and methods for making and using interconnections and methods for making these interconnect assemblies.
There are numerous interconnect assemblies and methods for making and using these assemblies in the prior art. Interconnect assemblies for making electrical interconnections with semiconductor integrated circuits must support the close spacing between interconnect elements, sometimes referred to as the pitch of the interconnect elements. Certain interconnect assemblies perform their functions through testing and the useful life of the integrated circuit. One type of interconnect assembly in the prior art uses a resilient contact element, such as a spring, to form either a temporary or a permanent connection to the contact pads on a semiconductor integrated circuit. Examples of such resilient contact elements are described in U.S. Pat. No. 5,476,211 and also in co-pending U.S. patent application entitled xe2x80x9cLithographically Defined Microelectronic Contact Structures,xe2x80x9d Ser. No. 09/032,473, filed Feb. 26, 1998, and also co-pending U.S. patent application entitled xe2x80x9cInterconnect Assemblies and Methods,xe2x80x9d Ser. No. 09/114,586, filed Jul. 13, 1998. These interconnect assemblies use resilient contact elements which can resiliently flex from a first position to a second position in which the resilient contact element is applying a force against another contact terminal. The force tends to assure a good electrical contact, and thus the resilient contact element tends to provide good electrical contact.
These resilient contact elements are typically elongate metal structures which in one embodiment are formed according to a process described in U.S. Pat. No. 5,476,211. In another embodiment, they are formed lithographically (e.g. in the manner described in the above-noted patent application entitled xe2x80x9cLithographically Defined Microelectronic Contact Structuresxe2x80x9d). FIG. 1A illustrates an example of resilient contact elements which are formed using a technique described in U.S. Pat. No. 5,476,211. FIG. 1B shows an example of a resilient contact element which is formed using lithographic techniques such as those described in the above-noted U.S. patent application entitled xe2x80x9cLithographically Defined Microelectronic Contact Structures.xe2x80x9d In general, resilient contact elements are useful on any number of substrates such as semiconductor integrated circuits, probe cards, interposers, and other electrical assemblies. For example, the base of a resilient contact element may be mounted to a contact terminal on an integrated circuit or it may be mounted onto a contact terminal of an interposer substrate or onto a probe card substrate or other substrates having electrical contact terminals or pads. The free end of each resilient contact element can be positioned against a contact pad on another substrate to make an electrical contact through a pressure connection when the one substrate having the resilient contact element is pressed towards and against the other substrate having a contact element which contacts the free end of the resilient contact element.
It will be appreciated that in certain instances, it may be desirable to secure the free end to the corresponding contact element by an operation such as soldering. However, in many instances, it is appropriate to allow the contact to be made by pressure between the two substrates such that the contact end of the resilient contact element remains free.
The resilient contact elements are useful for making electrical contacts because their resilience maintains pressure for good electrical contact and because they allow for tolerance in the vertical or Z direction such that all contact elements will be able to make a contact even if their heights vary slightly. However, this pressure sometimes leads to the deformation or degradation of resilient contact elements as they are compressed too much in the vertical direction. One approach to prevent the deformation or degradation of such resilient contact elements is to use a stop structure on one of the two substrates. The stop structure effectively defines the maximum deflection of the resilient contact element such that each of the resilient contact elements is prevented from overflexing (undue deflection) or being destroyed as a result of the two substrates being pressed toward each other. FIG. 1A shows an example of an integrated circuit having contact pads 103 and having, for each of the contact pads, a resilient contact element 110 mounted thereto. A plurality of stop structures 104 and 105 are disposed on the surface of the integrated circuit 102. These stop structures will prevent undue deflection and may engage another substrate which is pressed towards the surface of the semiconductor integrated circuit 102.
FIG. 1B shows an example of a lithographically defined resilient contact element on a substrate, such as a semiconductor integrated circuit 120. The integrated circuit includes on its surface a stop structure 150.
The lithographically defined resilient contact structure of FIG. 1B includes an intermediate layer 123 which makes an electrical interconnection with the bonding pad 122 through an opening in the passivation layer 121 on the surface of the substrate of the integrated circuit 120. A first metal layer 125 and a second metal layer 126 are then formed to create a beam having a step 128 and a beam portion 127. In this example, the beam portion is substantially parallel to the surface of the substrate 120. A tip structure including components 181, 182, 183, 184, and 185 is then subsequently mounted to the end of the beam 127 to create a resilient contact structure. Further details concerning methods for creating and using such lithographically defined resilient contact structures are described in the co-pending U.S. patent application entitled xe2x80x9cLithographically Defined Microelectronic Contact Structuresxe2x80x9d which is referred to above and which is hereby incorporated herein by reference. While this lithographically defined resilient contact element provides the advantage that it can be formed lithographically using modern photolithographic techniques which are prevalent in the semiconductor industry, there are certain disadvantages with this type of resilient contact element. For example, when a force F as shown in FIG. 1B is applied downwardly against the tip 185, a torqueing action occurs at the base of the resilient contact element. This torqueing action results from the pressure contact which occurs when a contact element on another substrate is pressed towards the tip 185. This torque at the base tends to place stress at the base and along the beam portion. If the beam portion 127 is a rectangular shape, this results in the stress being localized at the portion of the beam which is next to the base of the resilient contact element. While the stop structure 150 provides some assurance that certain levels of stress will not be exceeded, there are still certain concentrated areas of stress, as a result of the rectangular shape, which must be accounted for when designing a resilient contact element. Typically, accounting for these concentrated areas of stress requires increasing the use of the amount of materials at certain points in the resilient contact element. This in turn may limit the ability to design resilient contact elements to be smaller. This is particularly undesirable as the sizes of structures on semiconductor integrated circuits are being reduced over time.
Thus, it is desirable to provide an improved resilient contact element.
The present invention provides an interconnect assembly and methods for making and using the assembly. An exemplary embodiment of an aspect of the invention includes a contact element which includes a base portion adapted to be adhered to a substrate and a beam portion connected to and extending from the base portion. The beam portion has a beam geometry which is chosen to optimize stress. The beam portion is in one embodiment substantially triangular in shape and is adapted to be freestanding.
An exemplary embodiment of another aspect of the invention involves a method for forming a contact element. This method includes forming a base portion to adhere to a substrate of an electrical assembly and forming a beam portion connected to the base portion. The beam portion has a beam geometry which is chosen to optimize stress. The beam portion extends from the base portion and is in one embodiment substantially triangular in shape and is adapted to be freestanding.
In another example of the present invention, a resilient electrical contact element includes a base portion which is attached to a substrate and a beam portion which is connected to and extends from the base portion. The beam portion is adapted to be free-standing and has a beam geometry which is selected to produce a substantially optimized stress parameter given a desired size constraint of the beam portion and a desired spring constant (e.g. spring rate) for the resilient contact element. In one embodiment of this example, the geometry is selected to improve performance of the resilient contact element over a cantilever beam which has a substantially constant cross-sectional area. The performance may be improved by, for example, substantially evenly distributing stress throughout the beam when it is deflected.
It will be appreciated that in certain embodiments of the invention, a plurality of contact elements are used together to create an interconnect assembly.
Various other assemblies and methods are also described below in conjunction with the following figures.